Preparation Of Covalent Organic Frameworks And Its Composite Material Supported Pd Catalyst And Its Application In C-C Coupling

C-C bond is the basic structural unit for the construction of organic compounds,and its construction method is the focus of organic synthetic chemistry.C-C bond formation catalyzed by transition metals has been widely and deeply studied,and has become the most common and efficient method for constructing C-C bonds.Classical C-C bond formation reactions catalyzed by transition metals include Suzuki-Miyaura coupling reaction,Heck coupling reaction,Sonogashira coupling reaction and Stille coupling reaction,etc.Although homogeneous transition metal catalysts have high catalytic efficiency,they are difficult to separate from substrates,trace metal residues and can not be reused.In contrast,the supported catalyst can better overcome the above shortcomings.Relevant research has aroused great interest of researchers,and the design of green,efficient and stable supported catalysts has become a hot spot of current research.Covalent Organic Frameworks(COFs)are two-dimensional or three-dimensionalcrystalline Organic porous polymers with highly ordered network structures.It shows excellent performance in many fields and has excellent application prospect.Especially in the field of heterogeneous catalysis,COFs has the characteristics of stable skeleton structure,large specific surface area,abundant coordination atoms and predesigned pore size,making it an ideal support for supported catalysts.In this context,three different COFs and COFs composite supported palladium catalysts were synthesized and used to catalyze different reactions.The main research content of this paper is as follows:(1)COF-TM was synthesized by condensation reaction with melamine and 1,3,5-trimesoyl chloride as the basic structural units of COFs.Then,Pd-COF-TM catalyst was prepared by impregnation method.The elemental composition and morphology of COF-TM and Pd-COF-TM were characterized by FTIR,XRD,XPS,SEM and N₂adsorption and desorption techniques,respectively.The catalyst Pd-COF-TM can catalyze Suzuki-Miyaura coupling reaction in water phase efficiently at room temperature.The catalyst Pd-COF-TM showed excellent catalytic activity and cyclic stability,and the catalyst could be reused for at least 9 times.(2)The PGS/COF composite was successfully synthesized by covalently grafting COF onto the surface of amino-functionalized Palygorskite(PGS),and the transition metal palladium was supported on the PGS to obtain Pd-PGS/COF catalyst.Pd-PGS/COF has good catalytic activity in the C2 arylation of indole and has high tolerance to functional groups.It can be obtained in moderate to good yields for indole and its derivatives as well as various arylboric acid reaction products.The catalytic activity of Pd-PGS/COF remained after 5 cycles.(3)The fluorescent carrier material PGS/COF-SNW was obtained by connecting PGS with Covalent Organic Framework of fluorescence(COF-SNW)using silane coupling agent.The fluorescent material has good dispersibility in aqueous phase,and can quickly detect metal ions in water.It has certain practical application value.Through the fluorescence quenching phenomenon,it can be preliminarily determined that the metal palladium is loaded on the carrier COF-SNW without the help of physical characterization.Synthetic Pd-COF-SNW catalyst can efficiently catalyze Suzuki Miyaura and Heck coupling reaction in the aqueous phase.Pd-PGS/COF-SNW catalyst has a wide range of tolerance to reaction substrates with different functional groups,and the yield of related products can reach moderate to excellent.The catalyst Pd-COF-SNW is very stable and can be reused for 7 times without significant reduction in activity.